Apparatus for producing thermoplastic sheet articles

ABSTRACT

A machine for making articles from sheet thermoplastic material which is characterized by a group of openings provided in the smooth surface of the machine table and communicating with a source of hot gas fed under pressure to define a gas cushion supporting the blank above the table surface and assisting in the heating of the blank.

United States Patent [m I 1 I I 3,728,799

Strcltsov 1 Apr. 24, 1973 APPARATUS FOR PRODUCING References CitedTHERMOPLASTIC SHEET ARTICLES UNITED STATES PATENTS [75] Inventor:Konstantin Nilolaevich Streltsov, Le- 0 3/i934 W n 34/156 1,951,0 4 i ismgrad U'S'S'R' 2,848,820 8/1958 Wallin et a1. ..'....34/156 X [73]Assignee: Osboe 0pytn -k n tr k1 k bj 3,048,383 8/1962 Champlin ..34/l56X p0 razvmju mekhanmpmw 3,512,267 5/1970 Eichholz et a1. ..34/54 xtekhilllogii, g g PoREIoN PATENTS OR APPLICATIONS tre na rasnose 5 0e 5ossee, v U SS R 668,741 3/1952 Great Britain ..34/155 [22] Filed? p 1971Primary Examiner Carroll B. Dority, Jr. [21] AppL N0: 132,393Alt0rneyHolman & Stern [57] ABSTRACT [52] CL 34/151 34/148 263/6 4 4 Amachine for making articles from sheet ther- /317 moplastic materialwhich is characterized by a group I I of p g provided in the SmoothSurfaCe of the le 0 care machine table and communicating with a sourceof hot gas fed under pressure to define a gas cushion supporting theblank above the table surface and assisting in the heating of the blank.

2 Claims, 3 Drawing Figures Patented April 24, 19 73 3 Sheets-Shani i v3 2 3x Patented April 24, 1973 3,728,799

3 Sheets-Shoot 5 APPARATUS FOR PRODUCING THERMOPLASTIC SHEET ARTICLESBACKGROUND OF THE INVENTION The present invention relates to apparatusfor making articles of sheet thermoplastic materials.

The invention can be most effectively used for making bulky articles (upto 1.6 m long) of a complex shape.

PRIOR ART The known machine for making articles from sheet thermoplasticmaterials comprise a table capable of reciprocating movement and havinga smooth surface to accommodate a blank in the process of heatingthereof. From the table of the machine the blank is then fed formolding.

In the known machines, the blank is in close contact with the surface ofthe table and it is difficult to provide convective heat transferbetween the contacting surfaces. This results in nonuniform heating ofthe blank by thickness in due time and in reduction of the rate ofheating, therefore, decreasing the efficienty of the known machines.

Furthermore, it will be noted that during the nonuniform heating of thesheet material to a plastic state and in the process of molding thesethermoplastic materials, there are formed sections of concentratedstresses and local thinnings of the material which adversely affect thestrength of the prepared articles.

The heating of sheet thermoplastic materials, particularlyviscous-flowing materials, is associated with occasional adhesion of thematerial to the surface of the table which hinders the removal of theblank and the transfer thereof for molding.

To prevent this adhesion of the blanks to the smooth surface of thetable, the latter is covered with a special material (for example, glasscloth) having antiadhesive properties.

The use of an antiadhesive material is associated with the additionalconsumption of labor needed for replacement of the worn antiadhesivematerial after a certain period of operation of the machine.

To facilitate the removal of the blank from the table, the smoothsurface of the table is covered by a layer of powder such as talc beforeplacing the blank thereon. This introduces some inconveniences into theoperation of the machine.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present inventionis to eliminate the above mentioned disadvantages.

Another object of the invention is to provide a machine for makingarticles from sheet thermoplastic material having a table constructionfor placing the blank and transferring it to molding units which is moreefficient and convenient in operation than the known machines of thistype, while providing for high quality of the produced articles.

These and other objects are attained by providing such a device formaking articles of sheet thermoplastic materials in which, according tothe invention, the smooth surface of the table has groups of openingsconnected to a source of hot gas fed under pressure to provide a gascushion for keeping the blank above the table surface and assisting inheating of the blank.

Due to such a table construction the present machine provides for highquality of the produced articles while ensuring efficient operation andconvenient servicing of the machine.

Other objects and advantages of the invention will be apparent from thefollowing detailed description of one embodiment of the invention,reference being made to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the machineaccording to the invention, the view being partly in elevation andpartly in cross-section;

FIG. 2 is a top view of the machine, partly in section; and

FIG. 3 illustrates the table with a blank in the molding zone, the viewbeing partly in section and on an enlarged scale.

DETAILED DESCRIPTION OF THE INVENTION The machine for making articlesfrom sheet thermoplastic materials comprises a common frame 1 mounting afeeder A, a device B for heating a blank to an elastic state, a device Cfor forced molding of the heated blank, and a table 3 capable ofreciprocating movement guides 2 and having a smooth surface D (FIGS. 2and 3) for placing thereon a blank 4 in the process of heating the blankand feeding it for molding.

The feeder A consists of a collector of blanks having an arrangement forclamping one blank.

The device B consists of a known chamber-type heating oven.

The device C for forced molding of the blank heated to a plastic stateconsists of a press having a cross piece 5 provided wth a femaledie 6and a stationary plate 7 with a pneumatic chamber 8, an upper hydrauliccylinder piston unit 9, and a lower hydraulic cylinder piston unit 10.

According to the invention, provided in the smooth surface D of thetable 3 is a group of openings 11 (FIGS. 2, 3) connected to a source E(FIGS. 1, 2) of hot gas fed under pressure to define a gas cushionholding the blank 4 above the surface D of the table 3 and assisting inheating of this blank.

The gas is fed from the source E through a telescopic pipeline l2.Compressed air having a temperature higher than C may be used as thecushion gas. Nitrogen can also be used to advantage.

Such a construction of the table assists in the intensification anduniform heating of the blank in due time.

The gas cushion assists in a preliminary heating of the blank in theprocess of placing thereof above the surface of the table before feedingit into the device B, thus reducing the time of heating the blank insuch device.

In the device B, the chamber-type heating oven, the flows of thermalenergy and the gas cushion defined by compressed air heated to atemperature higher than 100 C), keeping the blank in a suspended state,create favorable conditions for heating the blank on two sides.

Thus, the rate of heat transfer through the thickness of the blankmaterial is increased providing for uniform heating of the blank. This,in the long run, eliminates the concentration of stresses and localthinning through the thickness of the material during the molding of thearticles, thereby providing for high strength of these articles, whichfact is of special importance in the process of production ofhigh'dimension articles having a length of about 1.6 m and a complexshape.

The present machine operates as follows:

Prior to the operation, the table 3 is in an initial position. The tableis conventionally divided into portions 1 and ll. The portion 1 is inthe feeder A and the portion ll in the device B for heating the blank toa plastic state. The first blank 4 is disposed on the portion 1 of thetable 3.

During the forward movement of the table 3 in the direction toward thedevice C, a known arrangement 13 for clamping the blank mounted in thefeeder A lifts the next blank 4a above the level of the table surfaceand holds it in this position.

The first blank 4 (FIG. 1) is fed into the heating device B, where it isheld above the surface of the table by means of an arrangement 14located in the heating device. Thereafter, the table is returned to theinitial position. in this case, the next blank 40 is placed above theportion l of the table, while the blank 4 located in the device B isplaced above the portion ll of the table and is supported there by theair cushion.

After completing the process of heating, the first blank 4 fed by thetable into the device C (FIG. 3) 3) for forced molding. In this case,the blank heated to a plastic state is removed from the portion ll ofthe table by means of a vacuum frame 15 disposed along the contour ofthe female die 6 and is held by this frame, until the molding isstarted.

Now, the next blank 4a disposed above the portion 1 of the table is fedinto the device B and is held there by the arrangement 14, while thefollowing blank fed from the feeder A is clamped by the arrangement 13and is held thereby in the above-the-table position.

Then, the table is returned to the initial position. In this case, theblank 4a disposed in the device B is placed above the portion 11 of thetable 3 and is supported by the air cushion, whereas the following blankheld by the arrangement 13 is supported on the air cushion of theportion l of the table.

Thereafter, under the action of the upper hydraulic cylinder 9, thecross piece with the female die 6 and the vacuum frame 15 carrying theblank 4 closes the pneumatic chamber 8 providing for hermetic sealing ofthe blank along the contour of the article being molded with thematerial being simultaneously squeezed out.

The force of the lower hydraulic cylinder piston unit 10 effectspreliminary drawing of the material, shaping of the fitting seats andforming the holes in the articles being molded.

The molding of the articles is effected by the pressure of a gaseousmedium fed into the pneumatic chamber 8.

After completing the molding, the prepared article is removed from thezone of the molding device C by means ofa pusher 16 (FIG.3).

Then, the table, moving in the direction of the device C, feeds the nextblank 4a for molding and feeds the following blank into the device B.

Such a sequence of feeding the blanks is effected during thereciprocation of the table in the process of making the articles.

The air cushion supporting the blank provides for convenient servicingof the machine, particularly when feeding and removing the blank in theprocess of molding, thus ensuring reliability of these operations andpermits the process of making the articles to be automated.

lclaim:

1. A machine for making articles from sheet thermoplastic materialcomprising feeding and heating means, said feeding and heating meansbeing in communication, a table having first and second portions locatedin the feeding and heating means when the table is in its initialposition, means mounting the table for reciprocating movement relativeto and between said feeding and heating means and a position adapted tosupply a shaping means, said table having a smooth surface for receivinga blank of thermoplastic material on the first portion thereof when thetable is in its initial position, said smooth surface being providedwith groups of openings throughout said first and second portions, measfor feeding hot gas under pressure to the groups of openings to providea gas cushion supporting the blanks above the smooth surface whichassists in a uniform heating throughout the cross-section of the blankwhen the blank is in the heating means and facilitates the removal ofthe heated blank from the table when the table has moved to a positionadapted to supply a shaping means.

2. The machine as claimed in claim 1, in which the table is defined by abottom wall, side walls, and said smooth surface constituting the topwall thereby providing a hollow body.

1. A machine for making articles from sheet thermoplastic materialcomprising feeding and heating means, said feeding and heating meansbeing in communication, a table having first and second portions locatedin the feeding and heating means when the table is in its initialposition, means mounting the table for reciprocating movement relativeto and between said feeding and heating means and a position adapted tosupply a shaping means, said table having a smooth surface for receivinga blank of thermoplastic material on the first portion thereof when thetable is in its initial position, said smooth surface being providedwith groups of openings throughout said first and second portions, meansfor feeding hot gas under pressure to the groups of openings to providea gas cushion supporting the blanks above the smooth surface whichassists in a uniform heating throughout the cross-section of the blankwhen the blank is in the heating means and facilitates the removal ofthe heated blank from the table when the table has moved to a positionadapted to supply a shaping means.
 2. The machine as claimed in claim 1,in which the table is defined by a bottom wall, side walls, and saidsmooth surface constituting the top wall thereby providing a hollowbody.